EMI is the unintentional radiation from electronic equipment which can interfere with external equipment such as radio, television, or computer units. Additionally, EMI radiation is capable of interfering with internal circuitry within the unit generating the EMI. In recent years, EMI has taken on greater importance because of the substantial use and increased density of electronic components which either generate or are susceptible to the effects of EMI. In computers and related fields which employ digital technologies, EMI is an extremely sensitive issue because of the increased speed of operation of digital circuits Modern digital circuits are capable of generating and processing signals with rise times as short as two nanoseconds. Unfortunately, these signals, while they represent a substantial increase in the speed of operation, are natural source of wide spectrum interference. One of the most troubling EMI problems therefore, is how to prevent these extremely fast digital circuits from interfering with the operation of other digital circuits positioned nearby.
Prior art techniques for containing EMI have been confined essentially to placing shielding screens in enclosures that surround the interference producing equipment. An alternative approach has been simply to place the interference producing equipment into a screened room. The type of screening generally employed is shown in FIG. 1 This type shielding is typically made of a conducting materials such as aluminum, and operates on the basic principal that the EMI will not pass through the apertures in the screen. For an in depth discussion on this phenomenon, refer to White, Donald R. J., Mardiguian, M. "Electromagnetic Shielding," Vol.3, Chapter 7, Interference Control Technologies Inc., Gainsville, Va., 1988.
Despite the plausibility of shielding screens, their use nonetheless suffers from various shortcomings. For example, installation is a labor intensive effort, which represents a substantial cost in the development of a shielded enclosure. While an improperly fitted screen will render an enclosure susceptible to intolerable levels of EMI leakage, more problematic are the effects of screen seal degradation under normal use and wear. Over time, the screen seals which fix the shielding screens within an enclosure degrade. Eventually, EMI leakage will necessitate refitting the entire enclosure. Because of the cost associated with each of these steps, there is a desire to avoid the use of shielding screens in the next generation shielded enclosure.